a. Field of the Invention
The present invention is in the field of semiconductor die packaging.
b. Description of the Related Art
Many types of electronic devices that include packaged integrated circuits (i.e., semiconductor dies), such as portable telephones, personal computers, and digital cameras, are being developed with increased functionality. To meet this trend, companies that assemble semiconductor dies into packages are developing semiconductor packages that are stackable. A stackable semiconductor package has the capability of having a second semiconductor package stacked upon it. Typically, solder balls of the second semiconductor package are fused to circuit pattern pads of the first semiconductor package, so as to be in electrical communication with the semiconductor die of the first semiconductor package and/or the input/output terminals of the first semiconductor package.
There are several difficulties associated with such stackable packages. For instance, the size of the solder balls of the second semiconductor package must large enough so that the second semiconductor package sufficiently clears a cap of plastic encapsulant on the first semiconductor package. On the other hand, the solder balls of the second semiconductor package cannot be too close together, i.e., cannot have too fine a pitch, or else the solder balls of the second semiconductor package may contact each other, forming an electrical short circuit. These constraints on the solder balls of the second semiconductor package limit the types of semiconductor packages that can be stacked and electrically coupled in the manner described above. Another problem with such stacked semiconductor packages arises during the stacking process. During stacking, the second semiconductor package may be misaligned such that its solder balls do not squarely rest on the pads of the underlying first semiconductor package. As a result, electrical failures of the stacked packages can occur.